Add a button to maniphest tasks to escalate security issues which need to be restricted.

Projects: Release-Engineering-Team, Phabricator, Security

Maniphest Tasks: T122556, T125104

Summary:
Refs T125104. This is based on example code provided by
@epriestley.

Test Plan:
Currently untested but it should be nearly
ready to go.

Reviewers: chasemp, csteipp, Luke081515

Reviewed By: csteipp, Luke081515

Subscribers: Negative24, chasemp, Luke081515, csteipp, epriestley

Differential Revision: https://phabricator.wikimedia.org/D113